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Changes in marine ecosystems from human stressors, and concerns over how species will respond to these changes have emphasized the importance of understanding and monitoring crucial demographic parameters for population models. Long-lived, migratory, marine vertebrates such as sea turtles are particularly vulnerable to changes. Life-history parameters like growth-in-body size can be largely influenced by environmental processes which can impact population growth. We analyzed a 40-year (1981-2021) capture-mark-recapture dataset from the protected UNESCO World Heritage Site, Aldabra Atoll, Seychelles, to estimate key population parameters, including body growth, for immature green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata). Curved carapace length (CCL) range was 34.3-110.9 cm (mean ± SD: 51.0 ± 11.4 cm, n = 1191) for green turtles and 28.7-89.4 cm (47.7 ± 14.4 cm, n = 538) for hawksbill turtles. Recapture events, with an 11-month minimum period, revealed a mean annual growth rate of 3.2 ± 1.5 cm year.sup.-1 for green turtles (n = 75) and 2.8 ± 1.4 cm year.sup.-1 for hawksbill turtles (n = 110). Hawksbill turtles exhibited a non-monotonic growth rate while no significant growth-size relationship was detected for green turtles. Green turtle mean annual growth per 10-cm size class was highest in the larger size classes (50â69.9 cm). Hawksbill turtle growth rate was highest in the larger size classes (50â69.9 cm) then declined in the largest size class (70â79.9 cm). Green turtles and hawksbill turtles may spend > 8 and 18 years, respectively, using Aldabra, Seychelles, as a foraging ground., Author(s): Cheryl L. Sanchez [sup.1] [sup.2] , Nancy Bunbury [sup.2] [sup.3] , Jeanne A. Mortimer [sup.2] [sup.4] , Luke A'Bear [sup.2] , Michael Betts [sup.2] , Rainer von Brandis [sup.2] [...]

Around the world, declines in the mean size of nesting sea turtles have been reported with concerns of a concomitant decrease in the reproductive output of populations. Here, we explore this possibility using long-term observations of green turtles (Chelonia mydas) at Aldabra Atoll, Seychelles. Based on > 4500 individual measurements over 21 years (1996-2016), we found the curved carapace length of nesting females declined by about 0.64 cm per decade, from 111.43 to 110.08 cm. For 391 individuals that were measured more than once with measurement interval of 2.8-19 years apart, the mean growth rate was 0.14 cm year.sup.-1. Comparisons between the size of adult females and males were based on 23 and 14 weight measurements, 107 and 33 carapace length measurements and 103 and 33 carapace width measurements, respectively, taken during 1981-1983. Adult females were larger than males, with the sexual dimorphism index, i.e. the ratio of size of the larger sex to the smaller, being 1.09 and 1.10 for carapace length and width, respectively, and 1.25 for weight. Smaller females tended to lay fewer eggs per clutch but the decrease in female mean size was accompanied by increases in numbers of turtles nesting annually, such that the estimated total numbers of eggs per year increased from 1.3 million to 2.0 million between 1996 and 2016. Therefore, a decrease in mean size of nesting females has not compromised egg production for this population., Author(s): Jeanne A. Mortimer [sup.1] [sup.2] , Jennifer Appoo [sup.1] [sup.3] , Bruno Bautil [sup.1] [sup.4] , Michael Betts [sup.1] , April J. Burt [sup.1] , Roselle Chapman [sup.1] [sup.5] [...]

To better understand dietary requirements, trophic shifts, and trophic interactions of the threatened green turtle (Chelonia mydas), we conducted a comprehensive global review and literature tabulation (177 studies) reporting diets of individuals > 25 cm carapace length. We analysed those studies involving natural sites and healthy animals that reported relative proportions of all diet components (67 studies, 89 datasets at 75 sites, 13 geographic sub-regions, 3 oceans). We compared diets by sub-region and foraging site relative to four diet components, i.e., seagrass, macroalgae, terrestrial plants (including mangroves) and animal matter. To assess sea surface temperature (SST) as an environmental driver, values were extracted from satellite data (single year) and site-specific observations (study durations) and examined relative to diet composition. Satellite data indicated that at warmer sites with temperatures > 25 °C ([greater than or equal to] 6 months annually), diet was predominantly herbivorous (mean = 92.97%; SE = 9.85; n = 69 datasets). At higher latitude sites and in cold-water currents with SST < 20 °C ([greater than or equal to] 6 months annually), dietary animal matter featured prominently (mean = 51.47%; SE = 4.84; n = 20 datasets). Site-specific observations indicated that SST had a small but significant effect on contributions of animal matter (r.sup.2 = 0.17, P = < 0.001) and seagrass (r.sup.2 = 0.24, P = < 0.001) but not macroalgae and terrestrial plants. Our study presents the first quantitative evidence at a global scale that temperature may be an important driver of omnivory, providing a new perspective on variations in green turtle diet, especially in light of global warming and climate change., Author(s): Nicole Esteban [sup.1] , Jeanne A. Mortimer [sup.2] [sup.3] , Holly J. Stokes [sup.1] , Jacques-Olivier Laloë [sup.4] , Richard K. F. Unsworth [sup.1] , Graeme C. Hays [sup.4] [...]

Green turtles (Chelonia mydas) are key herbivores of tropical and subtropical neritic habitats and play a major role in structuring seagrass meadows. We present the first detailed assessment of green turtle diet in the Western Indian Ocean using the gut contents of salvaged animals from three atolls in the Republic of Seychelles separated from each other by 400-825 km: Cosmoledo (adults, n = 12), Farquhar (adults, n = 33; immature, n = 1) collected in 1982-1983; and Desroches (immatures, n = 8) in 2016-2018. We report the first comparison of the diets of gravid females (n = 17), males (n = 26) and non-breeding females (n = 2) at sites providing both foraging and breeding habitat. Seagrass (mostly Thalassodendron ciliatum) dominated the diet, accounting for 95% of the mean gut content biomass for males and non-breeding females but only 58% for gravid females, alongside relatively large amounts of substrate (14%) and macroalgae (13%). Satellite tracking of post-nesting green turtles from Chagos Archipelago in 2016 located foraging sites at Farquhar Atoll that coincided with capture locations of 26 of the 33 adult turtles sampled there in 1983. In situ surveys of those sites in 2018 revealed extensive nearly monospecific beds of T. ciliatum. The prominence of seagrass in the diet of green turtles and connectivity between foraging and nesting habitats throughout the region illustrate the need to conserve and monitor seagrass habitats of the Western Indian Ocean especially in the context of changing green turtle population densities., Author(s): Holly J. Stokes [sup.1] , Jeanne A. Mortimer [sup.2] [sup.3] , Graeme C. Hays [sup.4] , Richard K. F. Unsworth [sup.1] , Jacques-Olivier Laloë [sup.4] , Nicole Esteban [sup.1] [...]